The goal of this project is to understand the role of individual nerve cells in the control of behavior. A certain species of marine invertebrate, Pleurobranchaea, has proven particularly useful in this pursuit. Like other gastropods, this animal has a relatively simple nervous system with large cells, which are readily identified and have consistent connections. Furthermore, Pleurobranchaea is especially useful because it is possible to study behaviors in a "whole-body preparation" which allows electrophysiological operations while the subject is virtually free to respond. In the last five years we have amassed a great amount of information concerning a particular behavior, feeding, and brain neurons which may control that behavior. In our proposed program we will enlarage this data base, integrate a wide variety of information and focus on specific cellular control systems. The purpose of the behavioral work is to provide useful paradigms for physiological investigations and to specify input-output requirements for brain cells. In our proposed experiments, we will try to determine whether classical and operant conditioning can be rigorously demonstrated in this species. We also plan additional studies of motor nerve output and muscular actions related to feeding. A survey of central neurons by electrophysiological and cell dyeing methods has resulted in a large data band stored on computer magnetic tapes. In the proposed experiments, this data will serve as a guide in locating relevant sensory, motor, and interneurons, and will continue to grow as data is collected. An important aspect of this work is the development and application of rigorous statistical methods for the identification of unique individual cells. Such identifications will provide a sounds basis for the main thrust of our work which is understanding neural "logic" responsible for complex patterns of behavior.